A secondary battery, or rechargeable battery, storage battery or accumulator is a group of one or more electrochemical cells, in which the electrochemical reactions are electrically reversible.
As is known, lead-acid batteries are made up of plates of lead and separate plates of lead dioxide, which are submerged into an electrolyte solution. The lead, lead dioxide and electrolyte cause a chemical reaction that releases electrons, allowing them to flow through conductors to produce electricity.
A lead-acid battery generally has a long life, or lifecycle, resulting in a large number of discharge/charge cycles. As the battery discharges, the acid of the electrolyte reacts with the materials of the plates, changing their surface to lead sulfate. When the battery is charged, the chemical reaction is reversed. That is, as a lead-acid battery is charged positive electrode active material is converted from lead sulfate/lead oxide to lead dioxide. Battery grids, and in particular positive battery grids, have been known to grow over time as the grid goes through its lifecycle.
One commonly known failure mode of a lead-acid battery occurs naturally through positive grid growth. Moreover, excessive cycling of the battery, excessive temperature, and over-charging can accelerate the rate of positive grid corrosion and thus grid growth.
Traditional battery grid manufacturing often takes special care to avoid significantly damaging the battery grid wire structure. As reported by Prengaman (Pb-80 Seventh International Lead Conference, Madrid, Lead Development Association, London, 1983, p. 34), deforming lead alloy materials after aging greatly reduces the subsequent mechanical properties and grain structure, as well as the corrosion resistance. Corrosion remains one of the most common failure modes of lead-acid batteries. Traditionally, therefore, battery grids are formed to avoid excessive corrosion and/or oxidation.
Many battery manufacturers compensate for grid growth by designing battery casings with an area of clearance to allow for grid growth over the course of the battery's life. Other battery manufactures attempt to mitigate the effects of corrosion by focusing development efforts on corrosion-resistant lead alloys for their specific grid manufacturing processes. Another alternative may be to add lead to the grid to reduce grid growth. However, the foregoing suffer from increased material and cost.
Traditional grid design often limits the size of openings in the grid based on manufacturing constraints and/or to ensure retention of the wet paste within the grid structure. Further, larger battery size may not be desirable or possible in many applications due to limited battery space allowed by a vehicle manufacturer. Additionally, while making the individual plates smaller within the existing battery case may provide the desired room for grid expansion, such an action may compromise capacity and high rate performance. Thus, the flexibility to provide more space within the container to accommodate grid growth is limited in traditional lead-acid batteries.